Feodra 11 should not have shipped with a beta but the previous stable
version.

That's really easy for you to say, considering you don't use
Thunderbird, and you have no information about the decision making process.

The information I used to make the decision was:
* The upstream release date was going to be within a week of
F11's release date, from a normally reliable source
* 3.0 had many desirable improvements to performance
* 2.0 would be EOL'd by upstream soon
* Thunderbird users tend to be in the "want upgrade now" camp
* Changing from 2.0 -> 3.0 after F11 was released is not something I
wanted to do
* Tb3 beta would affect a smaller portion of Fedora users anyway since
Thunderbird is _not_ the default mail client.
* Given initial testing by my team, and tracking upstream feedback, it
worked well enough and there were no major regressions over 2.0.

Given the situation and circumstances, with the information I had
available, I would make the same decision again.